Offices: * 1 Main Office + 1 Branch Office (different cities) * Each office is a site in the Active Directory * The offices are interconnected using a VPN over internet

Active Directory (2008 R2 native): * 1 single Forest (also single domain) * 2 sites (Main Office + Branch Office) * all the subnets are declared (Sites and Services) * 2 domain controllers at each office * All DCs are GC + DNS servers * The Schema and Domain Roles are in the DCs of the Main Office

Exchange 2010 (STD edition): * 2 CAS+HUB servers for each office (using NLB for each office), so each office has a CAS Array (array Main and array Branch) * 1 Exchange Server A for the Branch Office (for all the mailbox of this office) * 1 Exchange Server B for the Main office (for all the mailbox of this office) * 1 Exchange Server C running at the Main office (working as a Contingency Server, keeping a copy of all the mailboxes of the servers A + B) * The 3 Exchange servers are in a DAG * The witness server is running in one of the DC servers at the Main Office * MX servers: one in each office

Here´s the situation:

We deployed this infrastructure to have good performance (for the users) at each office, and also to have high availability. We placed the server C (the Contingency one) at the main office because it has a better infrastructure than the branch office.

My problem is the branch office: What we want (in a scenario where only the VPN goes down for 5-10 minutes, but both offices are up and running), is to keep the Exchange A at the branch office giving services to the users there (for internal email at the branch office and also sending email to the outside). We did the test (turning off the VPN) and the Exchange A became unavailable (I assume because it cannot contact to the res of the servers in the DAG + the witness). And of course the databases at the server C (the contingency one) mounted automatically.

My question are:

1) Can we mantain the Server A up and running for this particular situation (just VPN down for 5-10 minutes), and the users will continue having internal email for just that office? 2) Can we manage in a manual way the Failover over the server C (Contingency), and disable the Automatic Failover? It seems to be easy to disable the Automatic Failover but not easy to enable it. 3) Is DAC the Solution? or the Service Pack 1? Or Both?